Regression of meningioma tumor growth by combination therapy Fifteen percent of meningiomas have malignant characteristics and these aggressive invasive tumors are frequently fatal. Radiotherapy remains a major component of treatment modalities for controlling both malignant and benign meningiomas. In patients with residual or recurring benign tumors, there is increasing concern about radiation- related side effects that may occur even with highly accurate therapies such as radiosurgery. Besides therapeutic effect, recent evidence has shown that irradiation may promote malignant behaviors of cancer cells both in vitro and in vivo by activating several pathways involved in tumor invasiveness, angiogenesis and metastasis. Several studies, including ours, demonstrated significantly increased levels of uPA, uPAR, MMP- 9, and cathepsin B in malignant meningiomas. To determine the molecular interactions between radiation and uPA, uPAR, MMP-9, and cathepsin B in meningiomas, we propose the following specific aims: Specific Aim 1: Determine the effect of various siRNA bicistronic constructs combined with irradiation on meningioma cell growth, attachment, apoptosis, migration, and invasion in vitro. Aim 1a: Determine the effect of various siRNA bicistronic constructs combined with irradiation on the levels of uPA, uPAR, MMP-9 and cathepsin B in meningioma cell lines. Aim 1b: Evaluate the effect of various siRNA bicistronic constructs combined with irradiation on the molecular mechanisms of proliferation in meningioma cell lines. Aim 1c: Investigate the effect of various siRNA bicistronic constructs combined with irradiation on the molecular mechanisms of apoptosis in meningioma cell lines. Aim 1d: Determine the effect of various siRNA bicistronic constructs combined with irradiation on adhesion, migration and invasion in meningioma cell lines. Specific Aim 2: Evaluate the effect of various bicistronic siRNA constructs combined with irradiation treatment on meningioma tumor growth and angiogenesis in nude mice. Aim 2a: Determine the optimal dosage of various bicistronic siRNA constructs in the absence of irradiation for inhibition of pre- established intracranial tumor growth or invasiveness of human meningioma cell lines injected intracerebrally in nude mice. Aim 2b: Determine the effect of various bicistronic siRNA constructs combined with irradiation of pre-established intracranial tumor growth in nude mice. Aim 2c: Evaluate the effect of various bicistronic siRNA constructs alone or in combination with irradiation on cerebral angiogenesis in both in vitro and in vivo. The proposed studies should generate major insights into the pathogenesis of radiation-induced alterations in tumors and, in turn, should suggest novel targets for therapeutic interventions of meningiomas. PUBLIC HEALTH RELEVANCE: Fifteen percent of meningiomas have malignant characteristics and these aggressive, invasive tumors are frequently fatal. Radiotherapy remains a major component of treatment modalities for controlling both malignant and benign meningiomas. However, an increasing number of long survivors with secondary side effects from this treatment highlighted the need for development of novel therapeutic approaches. This proposal represents a combinational therapeutic approach using bicistronic siRNA. This strategy may improve radiotherapy outcomes for the treatment of meningiomas.